Ok gonna add 1 ab exercise to the end of each workout and treat it like any other muscle. i.e increase weight. There's like 1343324231412 to pick from though. I'll do some cable crunches today but any other recommendations robert 'washboard' scott?
haha! Not quite so washboard these days hence the recomp. Seeing as it's mass you're after, I would stick to lifts you can load up so you can get a hard as hell 8-12 reps. So things like
-full contact twists (ouch!) - http://www.youtube.com/watch?v=M2VmDm58MMI
-decline sit ups with a weight plate
-weighted roman chair crunches
-decline barbell crunches (good for serratus too which looks wicked when it's developed)
-ab wheel rollouts (more of a "core" exercise really but if you're not used to them you'll definitely see some growth)
but really I just think weighted cable crunches done either kneeling or standing should be your bread and butter. I've never found another exercise that challenges the abs like they do. The only problem is finding a weight stack heavy enough, most cable stations are too light (abs are strawng!)
The full contact twists do a good job of hitting the obliques too, I keep meaning to add them in on my leg day but never remember. They're quite an interesting mix between core and abs.
Now have at it!